Liquid crystal display (LCD) devices are display devices which control transmission/blocking of light (on/off of image display) by controlling the alignment of liquid crystal molecules having birefringence. Examples of display systems of LCD include twisted nematic (TN) mode in which liquid crystal molecules having positive dielectric anisotropy are twist aligned in the thickness direction of a liquid crystal layer; vertical alignment (VA) mode in which liquid crystal molecules having negative dielectric anisotropy are aligned vertically to a substrate surface; and in-plane switching (IPS) mode in which liquid crystal molecules having positive dielectric anisotropy are aligned horizontally to a substrate surface, and then a lateral electric field is applied to a liquid crystal layer.
Since LCDs are thin, light, and consume little power, and are therefore widely used as display equipment for televisions, personal computers, PDAs, and the like. Particularly in recent years, upsizing of liquid crystal display devices has been rapidly progressing, as represented by liquid crystal display devices for televisions and the like. For upsizing, the multidomain vertical alignment (MVA) mode is suitably used which can be produced in a high yield even if the device has a large area, and has a wide view angle. The multidomain vertical alignment mode is a mode in which liquid crystals having negative dielectric anisotropy are vertically aligned, and banks (line-shaped protrusion) formed on substrates or notches (slits) in electrodes are provided as structures for alignment control. In MVA mode, due to presence of such structures for alignment control, even if the alignment film has not undergone a rubbing treatment, the alignment direction of liquid crystals under application of a voltage can be controlled in a plurality of directions. Thus, MVA mode has a wider viewable angle as compared to conventional TN mode.
However, MVA mode has a problem that the display is dark. The main cause is as follows: Areas where linear protrusions (ribs) or slits are formed are overlapped with boundaries of alignment divisions to generate dark lines, and the dark lines reduce the transmittance during white display, resulting in a dark display. This problem is solved when the distances among ribs are sufficiently large. However, the number of the ribs which are alignment-controlling structures is reduced. As a result, a longer time is required for stability of the alignment of liquid crystals after application of a predetermined voltage, problematically increasing the response time. In order to solve the above problems and to enable high luminance and high-speed response, a technology for providing pretilt angles by use of polymers (hereinafter, also referred to as PSA (polymer sustained alignment) layers) is proposed (for example, Patent Literatures 1 to 5).
In PSA technology, a liquid crystal composition in which polymerizable components such as a monomer and an oligomer are mixed in a liquid crystal is enclosed between substrates, and the polymerizable components are polymerized in a state in which liquid crystal molecules are tilted by impressing a voltage between the substrates. Thereby, the liquid crystal has a predetermined pre-tilt angle even if the voltage impression is eliminated, and a liquid crystal alignment direction can be established. The polymerization of the polymerizable components is carried out by heat or exposure to light (ultraviolet light). Use of the PSA technology makes ribs unnecessary and improves the aperture ratio, and simultaneously imparts a pre-tilt angle smaller than 90° over an entire display region, enabling high-speed response.
Formation of a polymer wall between a pair of substrates in a liquid crystal display device has been known as a method for controlling the alignment of liquid crystals (for example, Patent Literature 5). The polymer wall in the method is a structure formed to surround a liquid crystal layer. Such a structure is substantially different from a PSA layer which is a thin layer formed on an alignment film.